1. Field of the Invention
The present invention relates to microcapsules filled with dye, used in an image-forming substrate, in which the microcapsules are formed as a layer of microcapsules, with an image being formed by selectively squashing and compacting the microcapsules in the layer of microcapsules, and also relates to a process of producing the microcapsules.
2. Description of the Related Art
In a conventional type of image-forming substrate coated with a layer of microcapsules filled with dye or ink, a shell of each microcapsule is formed from a suitable photo-setting resin, and an optical image is recorded and formed as a latent image on the layer of microcapsules by exposing it to light rays in accordance with image-pixel signals. Then, the latent image is developed by exerting a pressure on the layer of microcapsules. Namely, the microcapsules, which are not exposed to the light rays, are broken, whereby the dye or ink discharges out of the broken microcapsules, and thus the latent image is visually developed by the discharging of the dye or ink.
Conventionally, when a microcapsule is broken, it is impossible to adjust an amount of dye or ink that discharges out of the broken microcapsule. Namely, it is impossible to obtain a variation in density (gradation) of a dot to be produced by the broken microcapsules.
Also, each of the conventional image-forming substrates must be packed so as to be protected from being exposed to light, resulting in a wastage of materials. Further, the image-forming substrates must be handled such that they are not subjected to excess pressure due to the softness of unexposed microcapsules, resulting in an undesired discharging of the dye or ink.
Therefore, an object of the present invention is to provide microcapsules filled with dye, to be used in an image-forming substrate, wherein it is possible to discharge an adjustable amount of dye or ink from a microcapsule by squashing and compacting the same without any breakage of the microcapsule.
Also, another object of the present invention is to provide a process for producing the microcapsules as mentioned above.
In accordance with a first aspect of the present invention, there is provided a microcapsule comprising: a shell wall, formed of a shape memory resin, that includes bottomed fissures; and a dye encapsulated in the shell wall. The shell wall exhibits a temperature/pressure characteristic such that the bottomed fissures become through-hole fissures when the shell wall is squashed and compacted under a predetermined pressure at a predetermined temperature, whereby a seepage of the dye from the squashed and compacted shell wall via the through-hole fissures is adjustable.
The bottomed fissures may be formed as outer fissures which penetrate from an outer surface of the shell wall toward an inner surface. Also, the bottomed fissures may be formed as inner fissures which penetrate from an inner surface of the shell wall toward an outer surface thereof. Further, the bottomed fissures may comprise outer fissures penetrating from an outer surface of the shell wall toward an inner surface thereof, and inner fissures penetrating from the inner surface of the shell wall toward the outer surface.
The dye may be a liquid dye. Also, the dye may be a wax-type dye that exhibits a solid-phase at a temperature below the predetermined temperature. Namely, when the wax-type dye is heated above the predetermined temperature, this wax-type dye is thermally fused, and exhibits a liquid-phase.
In accordance with the first aspect of the present invention, there is provided a process for fissuring a shell wall, formed of a shape memory resin, of a microcapsule encapsulating a liquid dye, which comprises the steps of: irradiating the microcapsule with high frequency electromagnetic waves, such as microwaves, so as to thermally heat and expand the liquid dye; and penetrating outer fissures in the shell wall from an outer surface of the shell wall toward an inner surface of the shell wall by the thermal heating and expansion of the liquid dye. The thermal heating and expansion of the liquid dye is regulated such that the outer fissures do not completely pass through the shell wall.
In accordance with the first aspect of the present invention, there is provided another process for fissuring a shell wall, formed of a shape memory resin, of a microcapsule encapsulating a dye, which comprises the steps of: suddenly and drastically cooling the microcapsule such that only the shell wall abruptly hardens and contracts; and penetrating inner fissures in the shell wall from an inner surface of the shell wall toward an outer surface of the shell wall due to the abrupt hardening and contraction of the shell wall. The abrupt hardening and contraction of the shell wall is regulated such that the inner fissures do not completely pass through the shell wall.
In accordance with the first aspect of the present invention, there is provided still another process for fissuring a shell wall, formed of a shape memory resin, of a microcapsule encapsulating a dye, which comprises the steps of: cooling the microcapsule such that the shell wall exhibits a brittleness; exerting a pressing force on the microcapsule so as to deform the shell wall; and penetrating inner and outer fissures in the shell wall by the exertion of the pressing force on the microcapsule. The exertion of the pressing force on the microcapsule is regulated such that the inner and outer fissures do not completely pass through the shell wall.
In accordance with the first aspect of the present invention, there is provided still yet another process for fissuring a shell wall, formed of a shape memory resin, of a microcapsule encapsulating a dye, which comprises the steps of: treating the microcapsule with a corrosive liquid such that outer fissures are chemically developed over an outer surface of the shell wall; and washing off the corrosive liquid from the microcapsule before the outer fissures completely pass through the shell wall.
In accordance with a second aspect of the present invention, there is provided another type of microcapsule comprising: a shell wall, formed of a shape memory resin, that is formed with fine speckle-like depressions that do not completely pass through the shell wall; and a dye encapsulated in the shell wall. The shell wall exhibits a temperature/pressure characteristic such that the fine speckle-like depressions become through-holes when the shell wall is squashed and compacted under a predetermined pressure at a predetermined temperature, whereby a seepage of the dye from the squashed and compacted shell wall via the through-holes is adjustable.
Similar to the first aspect of the present invention, the dye may be a liquid dye. Also, the dye may be a wax-type dye that exhibits a solid-phase at a temperature below the predetermined temperature Namely, when the wax-type dye is heated above the predetermined temperature, this wax-type dye is thermally fused, and exhibits a liquid-phase.
In accordance with the second aspect of the present invention, there is provided a process for forming fine speckle-like depressions over an outer surface of a shell wall of a microcapsule encapsulating a dye, which comprises the steps of: cohering fine ceramic particles to the microcapsule, due to triboelectrification acting therebetween, such that a plurality of fine spaces are defined among the cohered fine ceramic particles around the outer surface of the shell wall; immersing the microcapsule with the cohered fine ceramic particles in a solvent over a predetermined period of time such that a plurality of fine speckle-like depressions is formed in the outer surface of the shell wall at locations corresponding to the plurality of fine spaces defined around the outer surface of the shell; withdrawing the microcapsule with the cohered fine ceramic particles from the solvent; and washing off retained solvent from the microcapsule with the cohered fine ceramic particles. The period of time, over which the microcapsule with the cohered fine ceramic particles is immersed in the solvent, is regulated such that the fine speckle-like depressions do not completely pass through the shell wall.